For cutoff and grinding machines of this kind, it is known to configure the arm out of two component sections movable toward each other in the longitudinal direction of the arm between which a belt tensioning device is arranged. The belt of the belt drive must be exchanged when the belt tensioning device has driven the arm sections apart to the maximum possible length of the arm. For this purpose, the user must press the arm together against the force of the tensioning device. This inconvenient and difficult measure considerably increases the difficulty of installing a new belt.